1. Field of the Invention
The present invention relates to a device for the tactile determination of a surface shape of a measuring object having a micro probe arm having a stylus tip.
2. Description of the Related Art
Optical measuring systems, which operate in a tactile and interferometric way, having a modulation interferometer and a reference interferometer situated downstream therefrom, are known for acquiring the shape, the diameter, and/or the roughness of surfaces. These measuring systems are used for optical distance measurement, for example, in quality control in the case of the measurement of surface geometries. Published European patent document EP 1 058 812 B1 describes such an interferometric measuring device for acquiring the shape or the distance, in particular of rough surfaces, having at least one beam generation unit, whose spatially coherent radiation is split in a measuring probe of the measuring device into a reference measuring beam, which is guided through a measuring reference branch and reflected therein, and a measuring beam, which is guided through a measuring branch and reflected on the rough surface, having a unit for modulating the light phase or for shifting the light frequency in accordance with a heterodyne frequency of a first partial beam in relation to the light phase or the light frequency of a second partial beam having a superposition unit for superimposing the reflected measuring reference beam with the reflected measuring beam having a beam decomposition and beam reception unit for splitting the superimposed radiation into at least two beams having different wavelengths and converting the radiation into electrical signals and having an analysis unit, in which the shape or the distance of the rough surface is determinable based on a phase difference of the electrical signals. It is provided that the radiation emitted by the beam generation unit is short-coherent and broadband with respect to time, that the beam generation unit, a beam splitter for forming the first and second partial beams, and the unit for phase modulation or frequency shifting are situated in a modular unit, which is spatially spaced apart from the measuring probe and is designed as a modulation interferometer, and that a delay element is situated in the modular unit in the beam path of a partial beam, which results in a difference of the optical path lengths of the two partial beams, which is longer than the coherence length of the radiation emitted by the beam generation unit.
Such interferometric measuring devices, which initially include two interferometers, may be constructed using different types of interferometers. Thus, the modulation interferometer may be constructed as a Mach-Zehnder interferometer, while the measuring interferometer or the measuring probe is constructed compactly, for example, as a Mirau interferometer. The interferometric measuring devices share the feature that a path difference registered in the first interferometer between two partial beams of a short-coherent radiation source is equalized again in the second measuring interferometer or the measuring probe and the partial beams may thus be moved into interference formation. The path difference registered by a delay element in published European patent document EP 1 058 812 B1 may be produced by partial arms of different lengths, through which the partial beams pass, as represented in published European patent document EP 1 058 812 B1 in a modulation interferometer constructed with light conductors.
To improve the measuring precision of the interferometric measuring device, attaching a reference interferometer to a second output of the modulation interferometer is known. It is optically constructed like the measuring interferometer, i.e., it equalizes the path difference registered in the modulation interferometer between the two partial beams again. The design construction of the reference interferometer differs from that of the measuring interferometer, however. The measuring precision of the interferometric measuring device may be improved by comparing the signals of the reference interferometer to those of the measuring interferometer. The path difference to be registered in the modulation interferometer depends on the structural design of the measuring interferometer or the measuring probe.
In addition to the described modulation interferometer, further optical, point-measuring probe systems and measuring methods for determining surface contours and roughnesses are known, for example, autofocus sensors, triangulation, chromatic sensors, and white light interferometers.
Furthermore, tactile probe systems, in which surfaces are sampled using a probe arm, are known. Furthermore, determining the movement of the probe arm by interferometry is known, as is implemented, for example, in the measuring device Form Talysurf Series 2 from Taylor Hobson. In a brochure of the shape measuring machine MFU 100 WP from Mahr, a probe system is described in which an optical or tactile probe arm is used. The analysis systems for the tactile and optical sampling are independent of one another.
In a related application of the applicant, a probe system of a measuring machine having a tactile sampling system having an assigned probe arm for the touching acquisition of the shape, the diameter, and/or the roughness of a surface and having an optical sampling system for the optical acquisition of the shape, the diameter, and/or the roughness of the surface are described, in which an identical optical measuring system having a shared optical analysis unit is used for the acquisition of the deflection of the probe arm of the tactile sampling system and for the optical acquisition of the shape, the diameter, and/or the roughness of the surface by the optical sampling system. The probe arm is mounted so it is rotatable in this case and its deflection is determined by interferometry.